Tissue blood flow is one of the most important physiologic parameters and also one of the most difficult to measure. The research proposed in this Phase II grant builds on the results on the Phase I feasibility study in the continued development of an integrated measurement system to provide both high precision, quantitative measurements of the local perfusion level, and rapid, real-time monitoring of transient perfusion variations. Recognizing that the thermal transducer is the fundamental determinant of ultimate measurement capabilities, the Phase I project addressed the design, fabrication and evaluation of a sensitive and linear thermal transducer as the basis of a clinical instrument for the measurement and monitoring of tissue thermal properties, including perfusion. These results will be more fully implemented in Phase II, where the thermal transducer will be integrated into the measurement instrumentation system to form the basis of an innovative and powerful measurement technique, with a projected ability to quantify perfusion to levels below 10 mi/100 gm-min and perfusion variations as small as 1-2 mi/100 gm-min. This will be followed by in vitro laboratory testing and evaluation, and later by clinical testing in several participating research laboratories in the Boston area. the results of this extensive development and refinement effort are expected to lead to a product of significant versatility and commercial potential.